Raman scattering in a locally anharmonic model with strong electron correlations

Stasyuk, I. V.; Mysakovych, T. S.

doi:10.1016/s0921-4534(00)00432-9

Cited by 2 publications

(4 citation statements)

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“…The above mentioned divergences on the temperature dependencies and an increase of the dielectric susceptibility which takes place in the vicinity of h = 0 and h = g values (for U → ∞, n < 1) are connected, first of all, with the polarization contributions Π 0 from the electron transitions between hole subbands (41) and (41) (or (41) and (41)). Just for h ∼ 0 and h ∼ g these subbands come nearer to each other.…”

Section: Thermodynamics Of Pem At Finitementioning

confidence: 93%

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Phase Transitions in Pseudospin-Electron Model With Direct Interaction Between Pseudospins

Stasyuk¹,

Havrylyuk²

1999

Condens. Matter Phys.

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A review of the present state of investigations of the pseudospin-electron model (PEM), which is used in the theory of strongly correlated electron systems, is given. The model is used to describe the systems with the locally anharmonic elements of structure represented in the model by pseudospins. The consideration is based on the dynamical mean field theory approach and the generalized random phase approximation. Electron spectrum and thermodynamics of the model are investigated; the cases of the simplified model, the model with strong interaction and the twosublattice model are studied more in detail. The phase transitions into other uniform or modulated states as well as superconducting phases are described; the criteria of their realization are established. Based on this, the description of structural and dielectric (ferroelectric type) instabilities, phase separation and bistability phenomena is given. A comparison is made with the thermodynamics of the Falicov-Kimball model (which can be considered as a particular case of PEM). The possibility of applying the PEM to the analysis of thermodynamics of the real HTSC systems is discussed. Attention is paid to the unsolved problems in the study of PEM.

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Section: Thermodynamics Of Pem At Finitementioning

confidence: 93%

“…In Refs. [40][41][42], the contributions into Raman scattering intensity, connected with the mentioned collective pseudospin excitations (that correspond to the phonon-like vibrations of anharmonic subsystems in the YBaCuO structures) and electron intraband and interband transitions, were considered.…”

Section: Introductionmentioning

confidence: 99%

Phase Transitions in Pseudospin-Electron Model With Direct Interaction Between Pseudospins

Stasyuk¹,

Havrylyuk²

1999

Condens. Matter Phys.

View full text Add to dashboard Cite

show abstract

“…The above mentioned divergences on the temperature dependencies and an increase of the dielectric susceptibility which takes place in the vicinity of h = 0 and h = g values (for U → ∞, n < 1) are connected, first of all, with the polarization contributions Π 0 from the electron transitions between hole subbands ( 41) and ( 41) (or ( 41 ) and (4 1)). Just for h ∼ 0 and h ∼ g these subbands come nearer to each other.…”

Section: Thermodynamics Of Pem At Finitementioning

confidence: 93%

Section: (The Quantum Monte-carlo Calculations)mentioning

confidence: 99%

Phase Transitions in the Pseudospin-Electron Model

Stasyuk

2007

Order, Disorder and Criticality

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November 18, 2018 21:48 WSPC/Trim Size: 9in x 6in for Review Volume stasyuk˙new Phase Transitions in the Pseudospin-Electron Model 3The pseudospin-electron Hamiltonian (in form (1) with inclusion only of the g-interaction) was used by Müller with the aim of describing the anharmonic vibrations in the oxygen subsystem of the high-T c superconducting crystals of the YBaCuO type. 1 The YBa 2 Cu 3 O 7−δ crystal is a typical and most studied example of such objects. The unit cell contains, besides two superconducting planes, the chain (at the δ ≪ 1 composition) elements Cu 1 -O 1 , connected by Cu 1 -O 4 -Cu 2 bridges with Cu 2 -O 2 plains through the apical oxygen ions O 4 . The vibrations of these ions along the c-axis (perpendicularly to the plains) exhibit a strong anharmonicity. Much evidence exists in support of this concept. One can mention the EXAFS data, 2,3 Raman scattering and dielectric measurements, 4,5,6,7,8,9 local polaron phenomena, 10,11 bistabilities in the normal phase region 12 as well as neutron scattering investigations 13 or the results of the first principle LAPW calculations. 14 Despite a certain ambiguity in the data, the conclusions were made about the existence of two different equilibrium positions of the O 4 ion. The local double-well picture as an approximate simplified model was supported by the oxygen O 4 vacancy effect on the positions of apical ions observed in Ref. [15].Moreover, a connection between positions of O 4 ions and electron states in Cu 2 -O 2 plains plays an important role in YBa 2 Cu 3 O 7−δ crystals. The data given in Ref. [16] point to the existence of a significant correlation between the occupancy of electron states of the Cu 2 ion and the R O4−Cu2 distance as well as to the decrease of this distance at the transition from the metallic orthorombic phase to the semiconducting one (that takes place at δ > δ * = 0.55). These and other similar facts suggest the presence of a large electron-vibrational coupling. In the pseudospin representation, when the pseudospin variable S z i = ±1/2 defines the positions of O 4 ions, it is described by the gS z i n iσ term. Consideration based on the PEM was applied to the HTSC systems starting from Refs. [1,[17][18][19][20]. Hamiltonian similar to (1) was used by Hirsch and Tang in the study of electron states in the framework of cluster calculations. In the context of the idea concerning the effect of anharmonicity on the superconducting transition temperature, 17,18,19,21 the possible connection between superconducting pairing and the lattice anharmonicity was considered by Frick et al. 22 (the quantum Monte-Carlo calculations). In what follows, the investigations of the PEM were devoted to the analysis of the electron spectrum, 23 the pseudospin and collective dynamics, 24,25 the charge and pseudospin pair correlations and the behaviour of dielectric susceptibility. 26

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Raman scattering in a locally anharmonic model with strong electron correlations

Cited by 2 publications

References 3 publications

Phase Transitions in Pseudospin-Electron Model With Direct Interaction Between Pseudospins

Phase Transitions in Pseudospin-Electron Model With Direct Interaction Between Pseudospins

Phase Transitions in the Pseudospin-Electron Model

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